Field of the Invention
The present invention relates to a semiconductor device and a control method thereof, and more particularly relates to a semiconductor device including an electrical fuse and capable of reading whether the electrical fuse is programmed or not without any erroneous determination, and to a control method thereof.
Description of Related Art
In a semiconductor device such as a DRAM (Dynamic Random Access Memory), a defective address is relieved by replacing a defective cell that does not operate properly with a redundant cell. For example, an electrical fuse is used for storing of defective addresses. The electrical fuse is made of a material mainly including copper, impurity-doped polysilicon or the like, and it is electrically conductive at an initial state. The electrical fuse is set to be a non-conductive state by generating heat by passing an electric current into the electrical fuse so as to disconnect it, and thus defective addresses can be stored in a non-volatile manner. Therefore, a desired address can be stored by providing a plurality of such electrical fuses and by disconnecting a desired fuse element. In this manner, an ordinary electrical fuse stores information in a non-volatile manner by changing the fuse itself from a conductive state to a non-conductive state (see Japanese Patent Application Laid-open No. 2007-329196).
However, as described in Japanese Patent Application Laid-open No. 2007-329196, there are cases where, even when known electrical disconnection or programming is performed on electrical fuses, the disconnection is not made as intended. That is, although disconnection processing is performed on plural electrical fuses, not all of the electrical fuses on which the disconnection processing has been performed are sufficiently disconnected. Consequently, insufficient disconnection causes the electrical fuses not to be completely non-conductive, and thus at the time of reading, there is a problem that electrical fuses that are supposed to be in a non-conductive or programmed state are erroneously determined as conductive or non-programmed state.
Meanwhile, similarly to the electrical fuse described in Japanese Patent Application Laid-open No. 2007-329196, there is known an anti-fuse as a type of an electrical fuse that uses electricity to change its state, which is conductive or non-conductive. Contrary to the electrical fuse of Japanese Patent Application Laid-open No. 2007-329196, the anti-fuse is an element that stores information by changing its state as a non-conductive or non-programmed state to a conductive or programmed state. Writing or programming of information into the anti-fuse is performed by insulation breakdown due to application of a high voltage. In the case of the anti-fuse, similarly to the case of the electrical fuse described in Japanese Patent Application Laid-open No. 2007-329196, in a strict sense, the result of the programming differs in each of electrical fuses. That is, there are various results such as an electrical fuse with a high conducting level (that is, its resistance is low), that with a low conducting level (that is, its resistance is high), or that having failed with conduction (its resistance is particularly high).